This invention pertains to rapid cycling particle accelerators having at least two accelerator rings, and in particular to such accelerators employing dipole electromagnet structures for confining the accelerated particles.
Rapid-cycling particle accelerators have at least one defined particle path, such as a circular ring or "racetrack". Acceleration is typically provided by a plurality of spaced-apart radio frequency resonating cavities which are placed about the ring. Thus, a particular particle or associated group or bunch of particles is accelerated in discrete bursts as it travels around the ring, typically at speeds approaching the speed of light. Particles traveling in the ring are subjected to centripetal forces during particle acceleration. If the particle beam is to be confined within the ring, these centripetal forces must be precisely balanced. The balancing force necessary for particle control is provided by electromagnets located adjacent the several accelerating portions of the ring. The present invention is directed to such electromagnets.
In one type of accelerator, the Rapid Cycling Synchrotron (RCS) located at Argonne National Laboratory, for example, discrete bunches of protons are accelerated for delivery at a designated target. The magnetic confinement of a particular proton bunch must be coordinated with the bunch's injection and ejection from the machine, as well as the duration of residence therein. While protons have been successfully accelerated at pulse repetition rates of 30 pulses per second, economical means of increasing the pulse repetition rate so as to satisfy demands for increasing particle intensity, have been sought.
This invention pertains to the economical design of new machines, and focuses on maximizing the pulse repetition rate that can be obtained from a system of given cost. The tradeoff involved in such designs centers around a balance of radio frequency accelerating voltage and the time rate of increases of the magnetic confinement field. Higher pulse repetition rates require more rapid cycling of the magnetic confinement fields of the machine. The shortening of the confinement field rise time, however, requires costly higher voltage rf accelerator equipment. The present invention is directed to the application of the aforementioned design principles to dual-ring particle accelerator machines.
Basically, dual-ring machines contain two accelerator arrangements which share common electromagnet confinement systems. Examples of a two-ring system employing dipole confinement magnets may be found in an article by R. J. Burke and M. H. Foss entitled "A Rapid Cycling Synchrotron Magnet With Separate AC and DC Circuits", IEEE Transactions on Nuclear Science, Volume NS-26, No. 3, June, 1979.
The arrangement described in the last-mentioned publication comprises several improvements in two-ring accelerators, such as a 75% reduction in tuning capacitance; isolation of ac currents from the dc magnet coils, and dc currents from the ac magnet coils; and coupling of the dc circuit to the ac circuit, while preventing coupling of the ac circuit to the dc circuit. However, this arrangement does not provide an improvement wherein B, the time-rate-of-change of the magnetic guide field, is reduced over conventional designs, with attendant reduction in rf accelerating cost. Improved B performance, as applied to single-ring synchrotron machines, is described in an article by M. Foss and W. F. Praeg, inventor of the present invention, entitled "Shaped Excitation Current for Synchrotron Magnets", IEEE Transactions on Nuclear Science, Volume NS-28, No. 3, June, 1981; and is also described in U.S. patent application Ser. No. 356,652, filed Mar. 9, 1982 in the name of W. F. Praeg. The last-mentioned improvement is provided by additional reactive components which are switched into and out of the magnet coil circuits at precise times, so as to provide a dual-frequency electromagnetic operating cycle. Such switching systems are, however, quite complicated and costly to construct.
It is therefore an object of the present invention to provide an improved electromagnet operating cycle for two-ring rapid-cycling particle accelerators employing dual-aperture dipole confinement/guide magnets, wherein the improvement of the operating cycle includes an extended acceleration period and a shortened reset period.
It is another object of the present invention to provide a dual-aperture dipole circuit having a second harmonic component which reduces the time-rate-of-change of magnetic guide field, thereby reducing the associated particle accelerating system rf power requirements.
Yet another object of the present invention is to provide a dual-aperture dipole magnet system wherein the ring magnets have less magnet iron, and the magnet coils have less copper, compared to conventional designs which utilize separate magnets.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.